1. Field of the Invention
The present invention relates to a multilayer ceramic capacitor and a board for mounting the same.
2. Description of the Related Art
A multilayer ceramic capacitor, a laminated chip electronic component, is a chip-type condenser installed on a printed circuit board (PCB) of various electronic products such as imaging devices (or video display apparatuses) like liquid crystal displays (LCDs), plasma display panels (PDPs), and the like, computers, personal digital assistants (PDAs), portable phones, and the like, to charge and discharge electricity.
A multilayer ceramic capacitor (MLCC), having advantages such as compactness, guaranteed high capacitance, and ease of mountability, may be used as a component of various electronic devices.
The MLCC may include a plurality of dielectric layers and internal electrodes, having a structure in which internal electrodes having different polarities are alternately laminated between the dielectric layers.
The dielectric layers have piezoelectric and electrostrictive properties. Thus, when a direct current (DC) or alternating current (AC) voltage is applied to an MLCC, a piezoelectric phenomenon occurs between internal electrodes, generating vibrations.
Vibrations may be transferred to a PCB on which the MLCC is mounted, through external electrodes of the MLCC, inducing the entirety of the PCB to become an acoustically radiating surface to generate vibratory sound as noise.
Vibratory sound may correspond to audio frequencies ranging from 20 Hz to 2000 Hz, making users uncomfortable, and such a vibrating sound, which may cause discomfort to users, is known as acoustic noise, and research into methods of reducing acoustic noise is required.
Also, in the MLCC, an internal electrode, smaller than a ceramic sheet and has a predetermined thickness, is printed on a ceramic sheet and the ceramic sheets respectively having an internal electrode printed thereon are laminated, inevitably generating steps between margin portions and the dielectric layers on which the internal electrodes are formed, and such steps may be severe in the outermost portions of the internal electrodes.
With the steps, if a thermal shock is applied or if stress resulting from warped printed circuit board (PCB) with the MLCC mounted thereon is applied, portions of the dielectric layers are delaminated or cracks may be generated.
Then, moisture and other foreign objects may infiltrate into an exposed surface of the internal electrodes due to the delamination or cracks, to degrade insulation resistance, reliability, or the like. This problem may be aggravated in a high capacity product having a large amount of laminated sheets.
Patent document 1 below relates to an MLCC in which a lower cover layer is thicker than an upper cover layer, but without disclosing a limitation in numerical values with respect to a distance between the outermost end portion of an internal electrode and an end portion of an external electrode.